Locate "qtbase/src/gui/painting/qcoregraphics_p.h" and you will find an objective-c category for Apples NSImage

// -------------------------------------
@interface NSImage (QtExtras)
+ (instancetype)imageFromQImage:(const QT_PREPEND_NAMESPACE(QImage) &)image;
// -------------------------------------

Now imagine you have two plug-ins compiled with Qt. Let's say with plug_a with Qt 5.15 and plug_b Qt 6.2. When plug_b with Qt 6.2 itself calls ...
[NSImage imageFromQImage:myImage];
... it is not clear which Qt library (5.15 or 6.2) will be used. 

Apple warns about those problems
https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html

---> "If the name of a method declared in a category is the same as a method in the original class, or a method in another category on the same class (or even a superclass), the behavior is undefined as to which method implementation is used at runtime. "

We have some crashes with that current situations. At the moment we use the following workaround which is based on namespaces.

// -------------------------------------
#define QtExtras QT_MANGLE_NAMESPACE(QtExtras)
#define imageFromQImage QT_MANGLE_NAMESPACE(imageFromQImage)
#define imageFromQIcon QT_MANGLE_NAMESPACE(imageFromQIcon)

@interface NSImage (QtExtras)
+ (instancetype)QT_MANGLE_NAMESPACE (imageFromQImage):(const QT_PREPEND_NAMESPACE(QImage) &)image;
+ (instancetype)imageFromQIcon:(const QT_PREPEND_NAMESPACE(QIcon) &)icon;
+ (instancetype)imageFromQIcon:(const QT_PREPEND_NAMESPACE(QIcon) &)icon withSize:(int)size;
// -------------------------------------

FYI : vestbo